Potentiometric aptasensing of small molecules based on surface charge change

Solid-state potentiometric sensors based on surface charge change are well-established tools for measuring ions and biological species. However, their use for detection of small molecules with high sensitivity and good selectivity is still elusive. In this work, a novel potentiometric aptasensing platform for small molecules is presented, using bisphenol A (BPA) as a model. The proposed sensor can be prepared by layer-by-layer assembling of carboxylated multiwall carbon nanotubes, poly(diallyldimethylammonium chloride) (polycation), and aptamer (polyanion) on the electrode surface. The presence of BPA induces the conformational change and detachment of the aptamer at the surface of the modified electrode, which leads to a variation of the surface charge (negative to positive) and therefore a potential change. The introduction of polyions can cause substantial charge change on the electrode surface, thus improving the sensitivity of the sensor. The morphology and electron-transfer properties of the electrode have been characterized. Under optimum conditions, the present sensor shows a stable response to BPA in the concentration range from 3.2 x 10(-8) to 1.0 x 10(-6) M with a detection limit of 1.0 x 10(-8) M. The proposed methodology can be used for sensitive potentiometric sensing of other small molecules involved in aptamer/target binding events. (C) 2017 Elsevier B.V. All rights reserved.